texts: Point spread function image deconvolution

texts:
I would like to deconvolve an image of Saturn.

I took an image of Saturn: Stack of 50 frames, the angular resolution of the original frames is 1.6''/pixel and the frames are scaled x4 before stacking.
I took an image of a star (Altair) using the same optical system and the same camera settings, stack of 50 frames, same resolution as Saturn. The separation between the star and Saturn is about 30°. I think that the shape of the star is mostly caused by the chromatic aberration of the scope.
I deconvolved saturn using Richardson–Lucy algorithm and the normalized image of the star as the point spread function (PSF) of the system.

However, the result is absurd (cf image). Why doesn't this method work? The image of the star seems pretty big. Do I miss a step to recover the PSF ?


texts: Is "Astronomy: A Physical Perspective" by M. Kutner written in 2003 a good introductory textbook? What other textbooks could you recommend? I want to study astronomy on my own but with scientific rigor (not just from popular science)


texts: This, of course, is a newbie question, as I am nothing more than a hobbyist. But I was quite surprised to see the recently-released "before and after" pictures of the so-called "Pillars of Creation" in the Eagle Nebula (here and here). For something that looks like such a "nebulous" cloud of gas (pardon the pun), I would have expected at least some visible sign of change in the 25 years between the two photos. But at the pixel resolution which I had available, I could not detect even the slightest difference between them. Of course, I am accustomed to terrestrial clouds which are in constant motion, so I (mistakenly?) expected something analogous at the astronomical level. Can someone provide, in layman's terms, how my understanding of this cosmological feature is deficient? In other words, how might I adjust my instinctive intuition that this object should be more dynamic? Is it just the sheer scale that I am not comprehending? (By the way: what is the distanse between the three spires, as compared to, say, our solar system?)


texts: Is this photocomposition of Andromeda's galaxy and the Moon accurate?

texts:
I recently saw the below image circulating around twitter/facebook/reddit. It is titled "Andromeda's actual size if it was brighter"

One of the comments provides a link to another comparison provided by APOD, and the following comment mentions that the first one I linked seems a bit off.

Is the first image accurate in term of relative sizes? What is the relative angular size of Andromeda's galaxy and the Moon?


texts: How much of carbon, sodium, silicon, and magnesium does the Sun have?

texts:
I've just begun learning of Astronomy and I can't figure out why any stars would begin their life with such elements if nuclear fusion hasn't created them.

Don't all stars begin life as Hydrogen?

I understand that the presence of these elements can change the luminosity of the given star. Is this also correct?


texts:
If the universe is expanding how come Andromeda is heading for us?
In isolated spatial areas does gravity overcome universal expansion?
What is the gravitational force between us and Andromeda?


texts: Reflector vs refractor in terms of magnification, which one wins?

texts:
I'm thinking about getting a telescope and i'm debating between these 2 telescopes: meade and orion. Theyre both the same price so this question is not about the money, but about getting the most out of your money. I like the Meade 102 mm (or 4 inches) because it is a refractor, which means it is more lightweight and compact. The orion starblast 4.5 on the other hand is a reflector and therefore more clumsy.

My question is, is a reflector necessarily better than a refractor in terms of magnification and sharpness of image? The orion does have a slightly bigger aperture (half inch bigger) but I don't think that makes a huge difference. The question really is, a reflector vs a refractor, which one is more desirable in terms of magnification, and how much of a difference does it make?

Just judging from the reviews it would seem like the reflector (orion) wins the fight. For example, Saturn's rings according to some reviewers are "clearly visible" in the reflector, but not so with the refractor which most reviewers agree, Saturn will be very tiny and the rings barely visible.

So will I settle for magnification if I get the refractor instead of the reflector, or are they basically the same and in that case I would choose the refractor (meade) over the reflector since it is more compact, and is also easier for beginners like me?


texts: Observing Comet 45P - reliable sources of position data

texts:
Yesterday night I have tried find comet 45P, that should be still easily visible with my equipment at hand, however I was unable to find it.
I used data provided by this website.

Today I've checked the website's data against the Minor Planets Center's data loaded into Stellarium (the program) and found the predicted positions of the comet to differ by more than 7°. That is totally unacceptable when trying to find the comet with a FOV of a few tens of arcminutes (the finder presumably is too light-weak).

So does anybody know a definite, reliable source for the position data of 45P? I'm gonna try again today anyway with the positions provided by Stellarium, but it might be good to have another alternative.


texts: In geocentric models, did the Earth rotate?

texts:
In geocentric models, did the Earth rotate around its axis?

I assume that if the Earth rotated around its axis, then the Sun would not have to orbit around the Earth at a very fast rate, whereas if the Earth didn't rotate, then the Sun would have to orbit the Earth every day.


texts:
I've seen elsewhere that if a terrestrial planet had a ring system, it would be very difficult (if not impossible) for life to evolve due to the shadow the rings would cast on the temperate zone in the winter time; it would be much, much colder.
Whether or not that is in fact the case, suppose there were some sort of...collision or other catastrophic event (such as a large asteroid getting too close and being torn apart in Earth's roche limit) that caused a ring system to form, even if only for a cosmically short period of time.

Would/could a ring system be created from such an event, and if not, are there any cases where it could happen?

If so, how long would it take the rings to form? How long would they last?


texts: Does the sun now 'bypass" some of the original zodiac constellations?

texts:
This question got me thinking of an interview of, or a talk by Neil deGrasse Tyson that I saw somewhere in the YouTube universe, giving a question one might ask to possibly challenge literal interpretation of one's astrological sign. For some reason I can't find it now, but I believe he said that currently the sun does not actually pass through all twelve zodiac constellations any more.

I'm not looking for opinions or any particulars about Astrology, please, just the science! (if there is some) If someone is familiar with the statement, I'd like to hear if I've got it right, and if it's due to proper motion, precession, redrawing/redefinition of constellation boundaries, or something else.


texts:
Could someone give the rough estimates of speeds of our travel through space?

I can easily find the two nearby ones:

Earth's own rotation - depending on latitude, up to 40,075 km/24h = 463 m/s
Earth's orbital speed around the Sun - 940 000 000 km/year = 29,786 m/s

Now how do these fare?

Motion of Sun within the arm of the galaxy, around the center of the galaxy?
Motion of the galaxy within the local supercluster?
(if possible to measure at all) movement of the supercluster within the universe?


texts: Question related to Sun rise and Sun set times

texts:
I am not sure whether this question is right or not so bear with me.

I understand 'Sun rise' and 'Sun set' is caused by the Earth's rotation.

I read that 'Sun light' takes around 8 minutes to reach Earth.

Every city in the world has its own 'Sun rise and Sun set' timings.

Lets assume the 'Sun rises' at 6 AM in 'City A'.

Does this mean that 'City A' sees/feels the light of the Sun which was in the sky @ 5:52 AM ?

In other words, does 'Sun rise' and 'Sun set' timings change according to 'light years'?


texts: Why do most galaxies or planetary systems have disc shape?

texts:
If we assume that mass was initially uniformly distributed in an area, then why does it flatten out after long time?

For example, consider our solar system or most galaxies out there.


texts: Explanation of the isochoric and isobaric instability conditions of interstellar medium gas clouds

texts:
The question Why are there no ISM clouds with temperatures between 100 and 6,000K? has an accepted answer of the form:

  Let $n$, $T$, and $x_i$ be the number density of hydrogen, the temperature of the gas, and $n_i/n$, where $n_i$ is the number density of the $i$th component of the interstellar medium. We can then write the criteria for thermal equilibrium as
  $$n^2\Lambda(n,T,x_i)-n\Gamma(n,T,x_i)\equiv n^2\mathcal{L}=0$$
  where $\Lambda$ and $\Gamma$ and the heating and cooling functions, respectively, and $\mathcal{L}$ is defined through those functions and $n$. If the equilibrium is unstable,
  $$\left(\frac{\partial\mathcal{L}}{\partial S}\right)<0$$
  for entropy $S$.

  This leads to different instability conditions, termed the isochoric and isobaric instabilities (Field (1965), $\text{Eq } 4a,4b$). These can be determined from the temperature, pressure, and density of the gas (also assuming that the gas can be approximated as an ideal gas).

which is not helping me understand why there aren't any beyond saying simply "because they are unstable."

I think the key is to understand what the "different instability conditions, termed the isochoric and isobaric instabilities" refer to - what those terms mean.

Is it possible to provide an approximate explanation of these two instability conditions in words that would not presuppose the reader has substantial depth in statistical physics?

There may in fact be an explanation in this answer, but I need something unwound a bit further. Also possible help in the several answers to this question.

edit: I've looked at this and this as well, and I know there is a region when the line labeled "heating rate" has a negative slope, but I don't understand what this actually means. Is there something like a gravitational effect (triggered by density) or a phase change or chemical reaction that 'triggers' this instability?


texts: How large part of the energy of the electromagnetic radiation in the universe is primordial

texts:
As I understand it there can be said to be two "kinds" of electromagnetic radiation filling up the universe. First you have the primordial radiation from a time soon after Big Bang. Then you have "newer" radiation from the fact that you start up with very diffuse clouds of mainly hydrogen that falls together and forms planets, stars, black holes etc. basically converting potential energy to heat radiation and in the stars you of course also have fusion producing heat that radiates away.

Can you say something like:

X percent of the energy of the electromagnetic radiation in the universe is primordial and (100 -x) percent of the energy of the electromagnetic radiation in the universe is of newer origin, and if so, what is X?

I mean if you "magically removed" all "primordial radiation" some 13 billion years ago we would still have a lot of radiation in the universe today.


texts: Will the E-ELT use Adaptive Optics at visible wavelengths?

texts:
In this recent BBC article I read that the European Extremely Large Telescope or E-ELT is in final design and is planned to be on line by 2024, and that (of course) it will rely heavily on adaptive optics (AO) technology.

In a great answer and discussion related to my previous question, it seems that while most AO is actually implemented for infrared imaging, work is being done to push the technology to visible wavelengths.

Will the E-ELT have AO available for visible light imaging in the beginning, will it be phased in later, or is there currently no plan for visible light AO?

note: Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing through dynamically deformable optics. AO is also implemented in radio astronomy computationally applied when data from arrays is combined, as described in this answer.

A drawing of the E-ELT from from Wikipedia (note scale of humans):


texts: How did Ole Christensen Romer measure the speed of light?

texts:
How did Ole Christensen Rømer, who in 1676, shortly after Galileo's death, was said to have measured the speed of light as 220,000 km/s by timing the orbits of Io around Jupiter?

My only guess is the moon Io orbiting Jupiter is simply a clock. It pulses away with an orbital period of 42 hours and provides to the earth, 21 hours of light each orbit; this does not change. Now, as viewed from "above" we go counterclockwise around the sun, and as we move towards Jupiter, the duration of light from Io would be less than 21 hours, whereas if we are moving away from Jupiter, the duration of light from Io would be more than 21 hours. Suppose we measure the time from Io's first appearance from behind Jupiter to its reappearance and call that its observed orbital frequency $f$ as opposed to its actual orbital frequency ${f_o}$ which is 1/42 hours.

He must have figured out the Doppler effect and this equation...
$$f = \left( {1 + \frac{{\Delta V}}{C}} \right){f_o}
% MathType!MTEF!2!1!+-
% faaagCart1ev2aaaKnaaaaWenf2ys9wBH5garuavP1wzZbItLDhis9
% wBH5garmWu51MyVXgaruWqVvNCPvMCaebbnrfifHhDYfgasaacH8sr
% ps0lbbf9q8WrFfeuY-ribbf9v8qqaqFr0xc9pk0xbba9q8WqFfea0-
% yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dc9Gqpi0d
% meaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaWGMbGaeyypa0Zaae
% WaaeaacaaIXaGaey4kaSYaaSaaaeaacqqHuoarcaWGwbaabaGaam4q
% aaaaaiaawIcacaGLPaaacaWGMbWaaSbaaSqaaiaad+gaaeqaaaaa!3BBB!
$$

I hashed through the numbers myself and I got an answer of about 10 minutes more or less from 42 hours depending on which way the earth is heading with reference to Jupiter.


texts: Do planets like Jupiter have a system of latitudes and longitudes (I believe yes)? So if yes, what purpose do they serve? Is there anything different in their purpose from Earth lat-longs? and What would be the average distance between each 1-degree latitude on Jupiter?


texts: Would two Earth-like planets on opposite sides of a Sol-like star at about 1 AU be a stable configuration?

texts:
Would two Earth-like planets on opposite sides of a Sol-like star at about 1 AU be a relatively stable configuration? I understand that there are tadpole-like orbits and the two planets may not stay exactly opposite each other, but oscillate around those position.

But given perturbations from other planets, say a Jupiter-like one at say 5 AU, might they eventually crash into each other, or would one end up moving to a higher orbit and the other to a lower orbit?


texts: What is the term for astronomical objects outside the solar system that are smaller than dwarf planets?

texts: Asteroids and comets only seem to refer to masses within the solar system, and it seems unclear whether planetesimal does.


texts: When did it take place, and what was the cause of the first blackhole in the universe?

texts: When did it take place, and what was the cause of the first back hole in the universe? Does this time precede stars collapsing as a result of old age?


texts: How can one explain the apparent motion of the Sun from a heliocentric point of view?

texts:
From a horizontal frame of reference, the path of the Sun looks like a part of a circle in a tilted plane, as shown in this picture:

If you go to a heliocentric system, one would say that this is because the Earth is rotating around it's axis. Is there any more detailed explanation of this change of reference?

So how can one explain in detail the following facts (seen from a geocentric point of view - horizontal reference system) starting from a heliocentric system and the fact that the Earth is rotating around it's axis:

Why is the path of the Sun a part of a circle?
Why is this path in a plane?
Why is this plane tilted?
How to get this "tilt-angle"?

Why does this motion seem to be uniform from an equatorial point of view, and can I neglect the ecliptic to understand the points above?

I tried to model it using a ball as Earth, attached a camera to it and used another ball as the Sun, but I didn't succeed in reproducing the effect of the apparent motion in this model. Perhaps there is any animation which makes the points above clear.


texts: Why is the height of a satellite greater than the apogee of its orbit?

texts: I read in the German Wikipedia for the Indian Technology Experiment Satellite, that the apogee (Apogäumshöhe) is 567 km, while the height of the orbit (Bahnhöhe) is 572 km. I had always thought that the apogee is the furthest point of the orbit from the Earth and I wonder how can there be a height greater than that.


texts: Where did the grand design spiral galaxy designation come from?

texts: What is the history behind the name that we gave to that class of galaxies?


texts: What are the Mathematical Algorithms/Formulas behind hindu Sunrise and Sunset Calculations?

texts:
There are differences between Astronomical Sunrise/Sunset calculation and Hindu calendar Sunrise/Sunset calculations. The astronomical algorithms to calculate the sunrise/sunset can be found over the internet. Here is a calculation that I followed to correctly calculate the astronomical sunrise/sunset time.
Sunrise and Sunset algorithm
In the Hindu calendar, sunrise/sunset is considered when the center of the Sun disk is at the horizon, also the refraction effect must be considered.
Sunrise on the Hindu calendar = Astronomical Sunrise + Time taken by the Sun to rise half of its diameter + Time taken by the Sun to rise further to neutralize the refraction effect.
Similarly, Sunset = Astronomical Sunset - Time taken by the Sun to set half of its diameter - Time taken by the Sun to set further to neutralize the refraction effect.
I am able to derive the Astronomical Sunrise/Sunset, but how to do the calculation for the following?:

Time taken by the Sun to rise half of its diameter.
Time taken by the Sun to rise further to neutralize the refraction effect.
Time taken by the Sun to set half of its diameter.
Time taken by the Sun to set further to neutralize the refraction effect.


texts:
I am a fifth (and last) year undergraduate student in Physics with good level of Mathematics formation and basic Astrophysics formation. I recently read some theories about Solar System formation and evolution and became interested in planetary stability, but I couldn't manage to get a good introduction to the topic.

I was wondering if there is a standard book or resource that approach this topic with precision that you could recommend. Any advice will be welcome.


texts:
Studying the stars classes for my homework (school) i learned that stars are classified by the spectral types (Harvard) and luminosity class (MKK) ..

So the sun is a star class G2V

But can not understand that clasificacion (far in the future) changes to MIII when his main sequence ends and begins to burn helium

What is the relationship there?
Would not it be more logical to classify stars according to their initial mass and any change that is made in the classification is related to the lifetime of the star?
sub classify them according to:
Fusion element: Deuterium, Hydrogen, Helium, etc.
And Remaining time fusing current element?

We are glued to the story?


texts: Books describing first-hand experience of astrophysicists finding planets without skipping actual maths

texts:
Are there good references of astronomical texts where we get a first-hand experience of astronomers uncovering astronomical gems using maths alone and not using observation. Observation may have been used later to validate the result.

In this book, there are several examples of astronomical jewels that were uncovered by the professionals. However the book shies away from describing the actual maths that aided the astrophysicists to make their conclusions and predictions that were later confirmed by experimenters.

However, how does a professional astronomer come to conclusions that there must be one more planet at so and so location? Are there books that uncover the exact line of thinking and maths that is involved  behind the works of the professionals?

I am not looking for a book which solves a toy problem rigorously using Newton's laws and then concludes that the 21st century astronomers use similar techniques at grander scales in their works. Though this is what is happening, i am looking for a more transparent description of how the pioneer discoverers make astronomical predictions with surety. The ideal place to look would be the research papers of these pioneers but is there a book that does that for many such achievements?


texts: Calculating the apparent magnitude of a satellite

texts:
I'm writing a program that involves calculating the apparent magnitude of satellites from a ground location. I currently have the intrinsic magnitude of the satellites and the solar phase angle in degrees. I can't seem to find a formula that works.

I tried

magnitude = intrinsicMagnitude - 15 + 5 * Math.Log(distanceToSatellite) - 2.5 * Math.Log(Math.Sin(B) + (Math.PI - B) * Math.Cos(B));

(B is the phase angle)

...but it does not work (it's returning numbers like +30). I know it's wrong because I'm comparing it to heavens-above.com satellite passes.

intrinsicMagnitude = Visual magnitude at 1000km away (Use -1.3)

distanceToSatellite = Observer distance to the satellite in km (Use 483)

B = This is what I am trying to figure out.

In the paper it says what this is but it says some other things that I do not understand. The phase angle you use to get this should be 113.

The target output of this equation should be around -3.


texts: Estimating the abundance of type-Ia supernovae using magnitude limited survey

texts:
I would like to estimate the fraction of type-Ia supernovae in a magnitude limited survey (only including those supernovae that are brighter than a certain than a given fixed apparent magnitude).

I currently have the following information:

Type-Ia supernovae are usually around 2.5 magnitudes brighter than core-collapse supernovae.
Volume limited surveys found that 30% of supernovae within a fixed distance from us are type-Ia.

How can I solve this problem using the above information? The formula for apparent magnitude $m = -2.512\log_{10}(d/10\mathrm{pc})+c$ seems like an obvious starting point, but doesn't seem to lead anywhere. A worked solution would be very helpful.


texts:
I've heard that there is something called the Great Attractor which seems to have some kind of gravitational influence on objects in the Universe.  Is this some kind of theoretical notion posited in order to help answer a question in Astronomy, or is there an actual object which is greatly attracting?

Or is this an obsolete notion?


texts: If Jupiter was placed in Mars' orbit, how would Jupiter appear from the naked eye?

texts: If Jupiter were as far from us as Mars, how big would it appear in Earth's sky? Would it appear huge, or would it be as small as a star?


texts: In the visible universe, we have a lot of matter to energy conversion going on in stars.  Is there an equivalent structure that is converting dark matter to dark energy?


texts: Hills' mechanism for making Hypervelocity Stars

texts:
In Hill’s mechanism, the gravitational tidal force of
  a single MBH disrupts an approaching binary. One star is captured on an eccentric orbit around
  the MBH and, by conservation of energy, the other star escapes with a final velocity equal to the
  geometric mean of the ∼$10^4$ km/s
  infall velocity and the ∼$10^2$ km/s binary orbital velocity.
  Hypervelocity Stars and the Galactic Center,
  Warren R. Brown, p.3

I don't understand how the high energy/velocity can be transferred to the star.

(Hills' 1988 Nature paper is still paywalled.)


texts: Does it make more sense to upgrade our existing telescope or to buy a new one?

texts:
We're at a bit of a crossroads here, since we're faced with what appears to be a tough choice.

We've got a Celestron 11" SCT tube with a Losmandy G11 equatorial mount, all bought in 1996. The mount has motors, but they're only capable of 5 tracking programs (Moon, deep space, etc). The tracking also doesn't appear to work quite well at the moment, but we may be able to fix that on our own.

We may, however, have an opportunity to acquire funding for an upgrade. We could upgrade the mount (or buy a new one), so that it is completely computerised and is capable of finding and tracking objects with ease. For that upgrade we've been given a ballpark of 2000$. I don't know where the number comes from, but let's assume we can have the desired upgrade with that sum.

Now, here's the question - wouldn't that money be better spent on buying another telescope, e.g. a Celestron Evolution 8 (same price range), which is already computerised, and is overall much easier to use? I realise there's a difference between 11" and 8", but I've had the opportunity to compare them in field and for our purposes, I couldn't find it.

We are a small astronomy club. Our activities with the telescope hardly go outside the scope of amateur astronomy - we look at the Moon, Saturn, Jupiter, sometimes Mars. We do sometimes look at, e.g. the Orion nebula, but so far that's the extent of our endeavours. We do not expect to transition to astrophotography, beyond what can be achieved with DIY solutions, nor do we use the telescope for research or data acquisition.

All things considered, which option - the upgrade to our existing telescope, or to buy a new one?


texts:
If the universe is expanding outward, what is the processes for one galaxy to get off track enough to collide with another?

Say, the Andromeda Galaxy and the Milky Way.


texts: What are the cloud-like blobs in the Martian southern hemisphere?

texts:
In a very recent edition of New Scientist, an article Mystery cloud-like blobs over Mars baffle astronomers (16 Feb, 2015), detailed that

  on 12 March 2012, amateur astronomers around the world noticed a strange blob rising out of the planet's southern hemisphere, soaring to 250 kilometres above the surface.

According to the article, this anomaly grew to be about 1000km across and even had 'fingers' stretching to space.

The article, details several theories (some being a bit wild) including atmospheric processes, aurora and stretching reality quite a bit - aliens (from the article, not me).

An image of the plume is shown below (a still image from this YouTube clip, which states that a 2nd plume was observed some months later:

The plumes appear to have formed in a region called Terra Cimmeria.

What are scientific theories, models etc for the formation of the cloud-like blobs in the Martian southern hemisphere?


texts: How did we differentiate lights from stars?

texts:
I got this question while watching the COSMOS TV series. I couldn't find the right answer in google.

I read about Stellar classification and it states that we can classify the stars based on their spectral characteristics. My question is how can we be sure of which particular star the light is coming from. Since Earth is getting light from so many stars How the the light is classified?  Even if we can get different spectra then how can find their exact sources?


texts: Do galaxies change shape and size over time?

texts: Galaxies come in different shapes and sizes. What factors determine the shape and size of a galaxy, and how can these change over time?


texts: Nothing is showing up in the viewfinder of camera when I try to do eyepiece projection photography.could I have something set up wrong?


texts: How energetic was the March 1989 geomagnetic storm?

texts:
In the March 1989 geomagnetic storm, how much energy was transferred to Earth's magnetosphere?

Most of the articles I find talk about initial solar flare energy, but I have no reason to assume all of that energy reached the Earth.


texts:
The closest star system to our Solar System is Alpha Centauri.

But is our Solar System the closest star system to Alpha Centuari?

If not, which star system is?


texts:
I was surfing the net for knowing the actual density of dark matter halo for a particular Mh(Mass of the halo) and finally, I got two equations:
 for pseudo-isothermal halo
and
 by NFW-profile
So, with which density distribution of dark matter halo should I go corresponding to any Mh?


texts:
I am an amateur astronomer looking to upgrade from a simple point and shoot camera looking through a Newtonian telescope to a more sophisticated set-up. I lecture at a local college and I am lucky enough that they may lend me a schmidt-cassegrain telescope (Celestron CPC series telescope).
I am looking to invest into my first DSLR camera and while I know Canon has their own dedicated astronomy camera (EOS Ra) such a camera is out of my budget. I have narrowed it down to four options and I would like to have more expert advice on which I should choose:

EOS 90D
EOS 77D
EOS 250D
EOS M50

I am lost to choose between those options. May you please shed some light? Thank you very much.


texts: What is the highest recorded temperature in space? I'm not asking about Planck temperature that is a fraction of a second before the Big Bang. I'm asking about the temperature that has been recorded by an instrument.


texts: What activities of human beings can be detected by aliens 1000 pc away?

texts:
Let's suppose they have similar technical level like us now.

In radio band, what is our earth like? What signals can be linked to non-natural behaviour?

How about optical band and other methods?

Simply:

How large a radio-telescope, 1000 pc away, would be needed to detect Earth's ambient human radio emissions?


texts: Stellarium 0.10.4: planet orbits change over time?

texts:
If I draw the orbit of Mars in stellarium 0.10.4 for 23 Sep 2015, it passes south of Chi Leonis:

If I advance the date to 17 Oct 2015, however, the orbit of Mars correctly goes right through Chi Leonis (Mars will occult Chi Leonis on 18 Oct 2015):

Is this a known bug in 0.10.4 that's been fixed? (I unfortunately can't upgrade)


texts: Kepler space telescope undetected planets

texts:
The Kepler space telescope detects planets based on the dip in brightness caused by planets moving past the star.

Wouldn’t that mean that there are an unknown amount of planets that have an orbit that wouldn’t be detected because their orbits don’t cross that path between the star and the telescope?


texts: What would a black hole merger look like?

texts:
Ship 1 is out side the black hole. Ship 2 is nearing a black hole. To ship 1 it would appear that ship 2 would be moving slower to the point it would seem like ship 2 stopped moving the closer to the black hole ship 2 gets.

I imagine that 2 naked black hole(an infinity dense point with out a surrounding black hole) merging would look like a blur from the speed of them, but and because of the time dilatation is this gif picture below a good rendering of how the merger would appear to ship 1? Then how fast does a black hole move when merging??


texts: In regards to the holographic principle, what exactly is information?

texts: I'm having trouble understanding what exactly "information" is in the context of the holographic principle suggested by string theory. Can it be equated to a matrix of ones and zeros? Does this information have its own laws of physics or are all laws of physics in our universe a result of this information, as in, does information supersede everything?


texts: How does the ESPRESSO Echelle spectrograph fold the spectrum so nicely?

texts:
The CBC News Technology and Science Q&A This ESPRESSO machine doesn't make coffee but scans the skies for habitable planets includes a nice description of ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) and links to the YouTube video Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations.

There's something really amazing about the way that the spectrogram has been folded so nicely on to this image. Is this what it looks like on a 2D detector? (sans colour of course)

I see what looks like eight distinct sections, and a really nice spacing between adjacent lines otherwise. How is this accomplished?

Click or open the image in a new tab for full size view (it's worth it; 1.8 MB, 1738x2530)

above: Frame grab from the video at about 00:55. Recorded with Python using this script, then extracting frames using this script in Blender. Click or open in new view for full size - it's worth it.

above: What an Echelle spectrogram "normally" looks like (again with added color). From the really interesting University of Virginia ASTR 3130 (Majewski) Lecture Notes.


texts: I've read that photon's have zero mass, hence no force is needed to accelerate them. But then the second question. How can gravity affect something which has 0 mass?. Yes, gravity(black hole) can bend space and time but how can 0 mass particle be affected by this?. What am i missing.?


texts: Does Jupiter lose some atmosphere at all?

texts:
I've hear of something like this: "All planets lose their atmospheres eventually and they become a barren rock if given enough time."

There are three types of atmospheric loss ways:

Jeans Escape: Temperature and escape velocity factors determine the gasses and the amount that's lost. Jupiter cannot lose atmosphere via Jeans escape because Jupiter has too high escape velocity and too high of a temperature.
Charge exchange: Solar radiation creates electrons and positively charged ions in upper atmospheres by tearing electrons off atoms or molecules. Subsequently, charge attraction and repulsion in collisions accelerates ions. Jupiter most likely cannot lose its atmosphere via charge exchange because its magnetic field is strong and extensive while no(little?) material escapes via polar wind.
Vertical atmospheric escape/impact erosion: Energetic objects that strike a planet erodes its atmosphere by creating a plume of heated gas. Jupiter does not lose its atmosphere via impact erosion because it has very high gravity and escape velocity. This pulls particles ejected by impact back into its atmosphere.

Since Jupiter doesn't lose atmosphere in the three types of atmospheric loss, how does it lose its atmosphere?


texts: Lunisolar calendar: what phase was the moon Y years ago on the spring equinox?

texts:
How would I go around answering these questions (e.g., for $Y=10,000$ -- IOW, historical observations are not available and the time is too long ago to rely on a fixed calendar):

How many days ago ($D$) was the spring equinox $Y$ years ago?
What phase (how many days from conjunction) was the moon on that day $D$?

Here is my "preliminary research":
Methodology
I suppose I could solve the 3 body problem (Sun, Earth, Moon) numerically backwards in time, but I suspect that the numerical errors and gravitation perturbations from other planets will accumulate rather quickly (how quickly?)
I could do arithmetic with the durations of lunation and year, but it appears that they are not as stable as I wish they were (are they?)
Software
Online calculators (NOAA, Stellafane) do not go that far back.
Presumably they rely on a version of Almagest but, again, it is not clear if these formulas are reliable for 3-5-10k year calculations.
Question:
How would I answer 1 & 2 above?
I am interested in both methodology (how it is done in general) and implementation (e.g., a program that would compute those numbers for me, given the value of $X$). It's okay to answer only a part of this, I will ask another, follow-up question.
PS. I asked this question on Math.SE and was told to "ask an astronomer".


texts: What are the so called clouds of dust and gas made of?

texts: We constantly read about "clouds of dust and gas" surrounding a (or being the initial state of a) star, but what elements constitute such dust and gas?


texts: Periodic error correction in automatic telescopes

texts:
I am starting a study on automatic telescopes and the correction of their periodic error.
I found two ways of correcting it : with a CCD camera and manually by recording the error. I was wondering if it could be possible to model the error by a periodic signal in order to add it to the entry signal then correct it with a low-pass filter or an other filter ?


texts: Are stars near the ecliptic the only stars from which Earth would appear to transit the Sun?

texts:
The majority of exoplanets we have discovered have been found by the transit method, in which a planet passes in front of its parent star and by analyzing the light curve we can deduct its characteristics.
Say there was intelligent life around a nearby star, could they only see the Earth transit in front of the Sun if they were located around the ecliptic?


texts:
The Wikipedia entry on NGC2516 mentions a mass value in the range $[10^5 - 10^6]\; M_{\odot}$. This seems like a rather enormous value for an open cluster.
In Jilinski et al. (2009) the authors state that:

The total mass of NGC 2516 is presently not well known. Values as low as 170 solar masses have been proposed by Pandey et al. (1987) and as high as about 1000 $M_{\odot}$ by Dachs & Kabus (1989). More recently a mass of ∼250 $M_{\odot}$ for this cluster has been quoted by Piskunov et al. (2008)

Anybody has a better/more recent estimate?


texts:
I’m taking Astronomy 101 this semester and this question on my homework is confusing me,
You may assume these conversions: 3.3 feet in 1 meter, 5280 feet in 1 mile, 60 seconds in 1 minute, 60 minutes in 1 hour, 24 hours in 1 day, 365 days in 1 6.
Assume you are in a spaceship that can cruise at an average of 15 km/s How long will it take you to get to our nearest star which is $2.5 \cdot 10^{13} {\rm miles}$ away? Speed of light in vacuum is 3.00 x 10^8 m/s. How long would it take light to travel that distance?
Any help explaining the steps to solving this would be appreciated because there will definitely be a question like this on the quiz
(It’s a time= velocity/distance question)


texts: Can we simulate Earth's gravity in space?

texts:
Earth gravity is 9.8 $ms^{-2}$

Gravity on ISS(international space station) is 8.2 $ms^{-2}$ approx.

As per this https://physics.stackexchange.com/questions/29929/gravity-on-the-international-space-station ISS never hit the ground because of it's vertical velocity.(free fall)

My question:

Can we create artificial gravity on ISS by using centrifugal force?
[Have anyone watched "The martian"? they have used this technique]


texts: When was the diameter of Titan first measured?

texts:
Titan is enshrouded in a thick opaque cloud of methane : with a telescope, you can't see the moon's surface. Because of this, from a distance, you can only see the diameter of the moon + its atmosphere, not the diameter of the moon itself.
When was the diameter of Titan first measured and how?


texts: How far out can the sun keep celestial objects revolving?

texts:
Astronomers define the Solar System as the distance under the influence of gravity from the Sun.

I read that the Oort cloud is probably the farthest object that surrounds the sun. The sphere of this icy cloud is thought to surround the Sun at up to a distance of 50,000 AU, making its total diameter nearly two light years.

How far can the sun's gravity extend to hold celestial bodies around it? The Oort cloud may be the known farthest body but its edge doesn't mark the end of the sun's effective gravitational pull.


texts: Is there a significant temperature difference on the moon from apogee to perigee or vice-versa?

texts:
Do those few thousand kilometers of difference going around the earth significantly affect the amount of thermal energy the moon receives from the sun to warm up its surface?

Also, are there more significant differences between these variables when the earth goes from perihelion to aphelion and vice-versa?


texts: How did the solar system get its angular momentum? Why did Earth not fall into the Sun at the start?

texts:
I know that Earth is always falling towards the Sun, but due to its sideways momentum it just misses always.  But how did it all start?  To go into detail, when the gas cloud with zero angular momentum collided, our solar system was made with planets and sun having their own angular momentum which makes them rotate.  But how did the revolution start in the beginning?  Were  they placed in such a position and distance that they started attracting each other but how ? .They were having only rotation .  But a revolution started which forced them to follow a elleptical path  so how this happened in the beginning?  Did some external force act on them and revolution started?  How was  this revolution started?

i have assumed dust cloud was having zero angular momentum but it can have any value that does not affect the question i think ?


texts: What might the surface of Jupiter's rocky core look like?

texts: Jupiter is posited, in some models, to have a rocky core about the size of a few Earths.  If we could see through the thick gaseous atmosphere, what topographical features might we find on the rocky core?  I know that no probe has ever sent data from Jupiter's (hypothesized) solid surface, and that orbiters probably can't penetrate the clouds to produce a topographic map, but do we at least have any educated guesses as to what sort of surface features are and are not likely to exist?  For example, given Jupiter's massive gravity, would the surface be extremely smooth?  Or would it not be out of the question to observe things like impact craters or mountain ranges?


texts: Hohmann transfer orbit (Earth-Jupiter system)

texts:
Consider the Hohmann transfer orbit of a probe launched from Earth to Jupiter. Assume the orbits of Earth and Jupiter are circular.

I want to calculate the following:

The semi-major axis and eccentricity of Hohmann transfer orbit from Earth to Jupiter.
The speed of the probe at Earth.
The launch speed of the probe from Earth to reach Jupiter.
The duration of the flight to Jupiter.
The elongation of Jupiter at launch to ensure that the probe arrives at Jupiter.

Here my attempt:

$a = \frac{1}{2}(r_E + r_J) = \frac{1}{2}(1+ 5.203) = 3.102 \text{ AU}, \ \ e = 1 − \frac{r_E}{a} = 0.677$
I am thinking of using the vis-viva equation but I don't know what I should use for $r$? Should I use $r_E$ = 1 AU for $r$ where $r_E$ is the average distance from the Earth to the Sun? Am I right? Please correct me if I am wrong.
I am thinking of using the escape velocity formula where $M$ is the mass of the Earth and $R$ is the radius of the Earth. Please correct me if I am wrong.
$t = \frac{1}{2}P = \frac{1}{2} \sqrt{a^3} = 2.73 \text{ years}$.
I really don't know how to do this question. Please help.


texts: What makes scientists already so certain that Comet C/2019 Q4 (Borisov) is a comet and not an asteroid?

texts:
US Naval Research Laboratory scientist Dr. Karl Battams has recently tweeted

  Unlike 'Oumuamua, whose asteroid-or-comet nature still gets debated, this one is definitely a comet. If it is unequivocally interstellar, it'll be fascinating to see how its composition (spectral properties) compare to the variety we see in comets from our own solar system.

Answers to Do astronomers generally agree that the distinction between comets and astroids is not so clear? suggest that the distinction can be a hard call sometimes, and some might instead call small solar system bodies formerly known as Prince comets and asteroids just that; SSSBs.

Question: What might cause astronomers like Dr. Battams be so confident that this object is a comet and not an asteroid, besides the fact that it's being called one? (Comet C/2019 Q4 (Borisov))

Is it just the orbit itself, or are there other observational data such as brightness in the infrared?


texts: Do Mercury and Venus exhibit retrograde motion?

texts:
This is more a terminology question, since Mercury and Venus certainly "move backwards" in the sky. The question is whether we call this retrograde motion. I'm referring to apparent retrograde motion here, not retrograde rotation.

I'm under the impression we don't, and reserve that name only for planets that are further away from the Sun than us; however conclusive evidence for whether this is (or isn't) the widely-accepted meaning for "retrograde motion" is hard to find.


texts: Do star systems stripped from galaxies have different expected behavior?

texts:
Another way of stating this question: Does the fact that a star system (or comparable concentrated mass) exists in a galaxy affect its long-term evolution, in terms of expansion, contraction, nebulation, etc.?

This question was inspired by a view of the "Umbrella Galaxy" where previous interactions have torn streams of stars far from the galactic disk.


texts: Could the closest approach of stable orbits of two earth sized planets allow life to jump between?

texts:
How close could two earth sized celestial bodies get in their nearest approach either as planets or moons around a larger planet?

Close enough for atmospheric interaction in a stable orbit at nearest approach, or for non-space-fairing species to somehow make the jump without cosmological assistance (aka asteroid impact)?

It seems just from using the roche limit of an earth to earth sized bodies any approach under ~20,000 km would be unstable in the long term, which is orders of magnitude beyond a normal atmosphere size.


texts: How much lighter would someone be on the Jupiter-facing side of Io?

texts: Io is the Galilean moon closest to Jupiter. Its average surface gravity is 0.183g and it has a tidal lock with Jupiter. So if you stood on the near side of Io at the equator, how much lighter would you be compared to average (say you weigh 18.3 pounds on Io, how much would you weigh due to Jupiter's gravity on Io's near side)? Jupiter has 318 Earth masses, this is why I think you'd be quite lighter on Io's near side on the equator.


texts: Undisturbed planetary alignment after galactic collision

texts: How do planets still orbit around the empty space where a black hole was after a black hole absorbs the milky way's black hole and keeps moving through space without disturbing surrounding planets that were orbiting that black hole?


texts: How do astronomers know if a planet is orbiting a star, or it's simply another star in the background?

texts:
For example, if astronomers photograph a "planet", which is in close proximity to a given star, then this "planet", could actually just be another "star" in the background, many light years away.

It might just be in the photograph by chance.

How can astronomers determine if this is, in fact, a planet orbiting that star or just another star many light years away?

For example, a common method to find planets orbiting stars is the transit method. ie, we can observe how the star appears to slowly decrease brightness, then increase back to normal again. This basically tells astronomers that this must be a planet.

But how do astronomers know that this isn't just the "front star" transitting a star "in the background"?


texts: Actual observable horizon for satellites on an orbit line map?

texts:
On a casual star walk, (for comparison of identifying different objects) I witnessed some meteors, quite a few satellites gliding on their smooth and straight trajectories, and some airplanes with their much brighter (sometimes blinking) lights, lower altitude and the characteristic sense of moving towards and away from me. Suddenly one of the satellites seemed as if its motion had been a bit jittery, and its path started to curve inwards in an asymmetrical, gentle and large C-shape. The airplanes made noise, this one did not. Visually perfectly identical with all of the normal satellites. I had never seen anything like that before so I wondered if it could've been some debris colliding into things, but probably not. The best explanation I have for now is that it apparently might have been a satellite on a Tundra or Molniya orbit, as their ground tracks aren't the usual straight or sine wave shaped trajectories that we're used to. Most satellite tracking websites either didn't seem to have tracking options for those special types at all, or you could only see their locations for now, not a custom time.

I'm in the capital city area of Finland, and when I saw the object, the time was 23:10 on the UTC+3 time zone, 12th of August 2016. Of what I found, the only strange looking ground track that comes even close would be Molniya 1-62, drawing a loop above Finland. What I can't find is a website that would allow me to rewind time to check where the satellite was at 23:10. But whether or not I should keep searching for that info.

I first have this question: If I look at the satellite tracks going across a map, how do I determine how far a satellite would be visible when viewed from the ground? If I looked at similar tracks for airplanes, it's much easier to understand that the ground area from which an airplane can be spotted doesn't span vast distances, but how this compares to a satellite is difficult to imagine as we don't perceive them in a three dimensional space, but spots gliding across the flat surface of a dome.


texts:
I've been playing around with Near Star Map, and I think I kind of want something more sophisticated, so for all stars within 100ly/30pc, is the following known?

velocity (it would be nice to have a vector field showing how fast in which direction stars are moving)
magnetic field intensity
estimated age
local ecliptic plane (and as much as that's meaningful for three-star systems with Poincare-befuddling orbital dynamics)


texts: Impact of inclined orbit satellite on a planet

texts:
If a satellite in an inclined orbit breaks up in orbit and multiple fragments hit a planet, do the individual fragments follow
1 a sinusoidal path
2 a geodesic ( or great circle curve)
3 a straight line
I'm having real problems trying to visualise this!
I realise the ground track of an inclined orbit follows a sinusoidal path but what happens when impacting a rotating planet?


texts: Why is iron responsible for causing a supernova?

texts:
Why is the element iron responsible for supernova? Can any star create more element than iron within the span of its life?

I understand that when star dies due to supernova, other elements are created (Gold and other 92 elements) due to more heat generated than required not only for fusion of Iron element but also for the fusion of higher element with each other.


texts: Where is the center of the Milky Way located?

texts:
I have downloaded a star database from this page (The HYG Database):
http://astronexus.com/node/34

And all the stars have (among other parameters) their XYZ coordinates in parsecs according to this definition:

  X,Y,Z: The Cartesian coordinates of the star, in a system based on the
  equatorial coordinates as seen from Earth. +X is in the direction of
  the vernal equinox (at epoch 2000), +Z towards the north celestial
  pole, and +Y in the direction of R.A. 6 hours, declination 0 degrees

The problem is: I cannot figure out how to calculate the XYZ coordinates of the center of the galaxy (the Milky Way). So the question is: What are the coordinates of the Milky Way center? (Or is it not possible to calculate it just with that information?). This is an example of the data:


texts: What is a typical polar angle of a pulsar beam?

texts:
I've found many articles on the geometry of pulsar beams, but I have not been able to find what would be a typical angle for the beam cone.  Illustrations I've found seem to look like it might be 1 or 2 degrees.
What range of angles might you expect to find for the polar angle of a pulsar's beam cone?


texts: Why does Io cast a hard shadow on Jupiter, but the Moon casts a soft shadow on Earth?


texts: Is it safe to view a solar eclipse with eyeglasses along with eclipse glasses?

texts:
In an article on Ars Technica about safely viewing a solar eclipse, they say this:

  First, what not to do: Don’t view the eclipse with your naked eye or unfiltered telescopes, binoculars, sunglasses (yeah, even if they’re really dark), camera lenses, or other optics devices. Don’t use anything that focuses light, even if you’re wearing eclipse glasses.

This may sound like a stupid question, but are eyeglasses (by which I mean, lenses to correct poor vision) safe to wear during an eclipse along with eclipse glasses? I don't know if the light focusing is strong enough to be concerned about.


texts: Finding individual band magnitudes: Why and how is the integration of individual flux values for each wavelength used?

texts:
What differentiates the distance modulus equation to find the difference between two apparent magnitudes? For example,

$$ m_1 = -2.5\cdot log_{10}\left(\frac{F_1}{F_2}\right) + m_2$$
leads to the following, in the U band:
$$\implies m_U = -2.5\cdot log_{10}\left(F_U\right) + C_U$$

and the relationship involving taking the sum of the fraction of the flux that a star outputs at each wavelength rather than the ratio between the fluxes of two stars, here in the UV band for example:

$$ m_U = -2.5\cdot log_{10} \left(\displaystyle\int_0^\infty F_{\lambda}S_U \,\, d\lambda\right) + C_U$$

*$S(\lambda)$ = the fraction of the star's flux detected at wavelength lambda.

Succinctly, what is the difference between the above two equations?

More specifically, how would this be used in a real-world situation to find the apparent magnitude of an object? My deduction is that apparent magnitude isn't as simple as taking the flux in a certain filter to find the apparent magnitude, and that each individual wavelength must be accounted for. However, with that notion, why can't we just remove the sensitivity function and change the bounds to those wavelengths within the U band?

The other option would be that this is just more accurate than taking the flux within the U band (referring to the above example), because you would take smaller intervals, possibly over 1 $\buildrel _\circ \over {\mathrm{A}}$ intervals since infinitesimal ones would be impossible.


texts: Could information be transmitted from inside a black hole using gravitational waves?

texts: Could you use gravitational waves to communicate from inside the event horizon of a black hole to someone who was outside?


texts: Why do the rings around the Gas Giants get their 'ring' shape?

texts: In our Solar System, all the gas giants have ring systems. However, why do these rings form rings and not a cloud of debris around the planet?


texts:
We know that a planet is formed from the nebula of gas and dust. Gravity pulls the particles together in a core. So we all know that the gas cloud is a cloud of hydrogen.

But how did water form? From where did oxygen come? How did it combine to make $\text{H}_2\text{O}$?


texts: Is there a link between the amount of swirling and vorticity in a gas giant's atmosphere and its distance to its Sun?

texts:
This is an empirical observation of mine:
I have noticed that out of the 4 gas giants in our Solar System, Jupiter's atmosphere has the most visible swirls and complex cloud patterns, followed by Saturn and then by Neptune (I have ignored Uranus here since I heard its heated more by the Sun than by its own internal heating)
These 3 planets also seem to be arranged in their distance to our Sun. I am assuming more heat from a Sun = more complex weather patterns due to interactions with the atmosphere
Does this mean that hot exo-planet gas giants would have extremely swirly, complex weather patterns?


texts: Is a white dwarf hotter than a Red Giant?

texts: From what I've read, white stars are hotter than red ones. But a white dwarf would have just heavy elements to fuse, so shouldn't it be less bright?


texts: How can a rotation period of a planet's satellite/moon be "chaotic" (like Hyperion around Saturn)?

texts:
According to wikipedia (see info below image) Hyperion's rotation period around Saturn is "chaotic".

What does that mean? The period (in days/hours) is different every rotation without any law helping to define it?

How can it be?


texts: Assuming a gas giant is primarily gaseous past our visibility, is it possible that a moon traveling at a sufficient velocity would be able to exist within the atmosphere, or would terminal velocity from the atmosphere prevent an object of that size from maintaining appropriate centripetal force? For example, Neptune has winds that are so fast they move beyond the speed of sound. Would a moon be able to exist in an environment like that?


texts: Are red giants stationary or do they move?

texts: A friend and I are having a friendly chat about this. They are stars so I'm claiming they still move in orbit.


texts: How much time passes in the outside universe when falling into a black hole?

texts:
If someone were to jump into a black hole, looking back at Earth, how far into the future would they see of Earth?  As I understand it, time would dilate approaching infinity as you approach the event horizon.  As I understand, time dilation would reach infinity for an infinitely small amount of time, but Planck time would probably prevent that infinity from arising.  How much time would pass in the outside universe as we fall in?  How far would we see into Earth's future, if we were looking back at it as we fell in?  This is further pondering my prior question and the answers received for:

Would time go by infinitely fast when crossing the event horizon of a black hole?


texts: How accurate are NASA's eclipse predictions?

texts:
NASA's predictions for the August 2017 solar eclipse show that about half of Kansas City will see a total eclipse and the other half won't (they'll just see a "near" total eclipse, perhaps even Bailey's Beads?).

I thought this would be a great way of testing how accurate NASA's eclipse path prediction is: have people in Kansas City report, with location, whether they saw a total eclipse or not (of course, many people in Kansas City will probably head into the total eclipse zone just to see it, but hopefully few will remain outside it).

It then occurred to me that someone must've already done this for previous eclipses (I know it's done for lunar occultations of other stars).

However, googling only tells me that NASA's 2017 path predictions are more accurate than ever before, but not actually HOW accurate they are.

Where can I find data about accuracy of eclipse predictions?


texts:
From reading various sources online, I see that some people talk about binary planets in very tight orbits (around 1 or 2 planet radii). I am wondering if it is possible for a binary planet (Double planet) system to exist at a much greater distance from eachother.

Setup: Binary planets orbit their star at 1.19AU. Planet 1 is 1.254 Earth masses and planet 2 is 0.8087 Earth masses. They orbit eachother with a apoapsis of 750,600km and a periapsis of 742,500km.

According to calculations, they are within the sweet spot of each other's hill sphere and of course far from the Roche limit.

Bonus info to further complicate the situation, the star system is a binary star system, Alpha Centauri. The planets orbit the A star and are well within the stable orbital region of that star and should theoretically not be majorly affected by the B star.

Is this a stable planetary system? Any reasons why it wouldn't work would be great.


texts: What exactly is the cause of blue light of ion (plasma) tails of comets? Somewhere I have read that the source of blue light are CO+ ions which has just acquired the missing electron and became neutral molecule CO. Is this correct?


texts: Why solar eclipse paths are symmetrical?

texts:
Reading upon the eclipse of March 20, 2015, I stumbled upon this page: http://www.timeanddate.com/eclipse/list-solar.html. What caught my eye is that for each year there are two eclipses whose paths are almost symmetrical relative to equator.

I'm just curious why that's always exactly so.


texts: Is there a single, most prominent helium line?

texts:
There's a prominent spectral line at ~1420 MHz caused by hydrogen.  From what I can tell, this is the most notable electromagnetic emission from hydrogen in radio astronomy.

Is there an equivalent helium line -- a single, prominent radio emission of helium in space?

(And are there equivalents for other elements too?)


texts: When do Mercury/Venus reach greatest elevation at sunset/twilight for a given location?

texts:
On what day does Mercury reach its greatest elevation (in degrees from
the horizon) at sunset a given location?

The obvious answer is the day of Mercury's greatest elongation from
the Sun, but, since the ecliptic is slanted with respect to the
horizon, I'm not convinced this is correct.

In other words, on the day after greatest elongation, Mercury's total
angular distance from the Sun will be smaller, but it's vertical
distance in elevation (for a given location) at sunset might be
higher.

Same question for Venus, and for when the sun is 6 degrees below the
horizon (ie, civil twilight), and for sunrise/dawn.

I'm guessing the date might vary based on position (mostly latitude) since the ecliptic's slant varies at different locations.

I googled and found nothing. My (preliminary and possibly wrong)
expierments with stellarium show that Mercury's elevation at sunset IS
higher 1-3 days after its greatest elongation, but by less than 1/2
degree.

So, it's possible that the date of greatest elongation is a close
enough approximation.


texts: The surface is freezing-nitrogen cold, but it's typical for the temperature to increase towards the core. What's the temperature of the core of Pluto? Is the planet icy and rocky all the way through? I wonder at the possibility if that frozen ice ball could have any internal heat at all?


texts:
The Luminosity of a star is proportional to the 4 th power of its temperature and square of its radius. Also the mass-luminosity relationship says that the luminosity of star is proportional to approximately M^3.5.
Consider a star in main sequence. It is in hydrostatic equilibrium so there is no collapse or expansion. Thus the Radius does not change much. Also the star is thermal equilibrium so the energy it generates equals the energy it radiates away. Thus the temperature must not change significantly.
Moreover the star is losing mass as energy due to fusion. Now if we consider the mass luminosity relationship here, then why is there a slight increase in luminosity in star during its stay in the main sequence. If it's losing mass then it should lose its luminosity as well, right?
Please tell me where I am going wrong in my reasoning.


texts: tiny diamonds in meteorite "signature of a long-lost planet": why come to Earth in 2008?

texts:
ref this paper in Nature re the Almahata Sitta 2008 meteorite shower.

I get that they're saying the diamonds could only have been formed within something the size of planet, which subsequently broke apart in the "early days" of the Solar System.

I get that Saturn and Jupiter are so massive relative to other Solar System bodies they've marshalled fragments into the Asteroid belt, Kuiper belt, outer disk. And that they're still disturbing those regions enough to occasionally pull things into a cometary orbit/become meteors.

This putative planet must have scattered everywhere when it first broke apart/lead to comets and meteors all over the place. But why/how did this fragment wait until 2008 to come to Earth? Where's it been for billions of years? Why didn't it either crash into something a long time ago; or form itself into a stable orbit?

Possibly related, as in: why haven't meteorites originating from early-formed planets all long gone extinct?


texts: Which database of celestial objects do stargazing apps use?

texts:
Stargazing apps such as Star Walk must have a database with a list of celestial objects, their names and details and each of their celestial coordinates.

I am interested to know which database these apps use as I am looking to build my own stargazing app for a computing project.

It would be great if someone could help me with this.

Thanks!


texts: Can there be planets, stars and galaxies made of dark matter or antimatter?

texts: We know that the universe has more dark and anti matter as compared to normal matter. Can there be dark matter galaxies or antimatter galaxies?


texts:
How would a person measure that he is at a planetary pole? My first inclination is to use a sextant to ensure that the Sun remains at a constant inclination. However, due to the orbit around the Sun and a possible planetary axial tilt, the Sun's inclination may vary over the course of the year and that could affect measurements if the length of the day is a significant portion of the length of the year.

A second inclination is to try to identify a pole star or at least the point about which distant stars rotate during the course of a planetary rotation. The observer could then (at least in theory) measure the inclination of this point assuming that planetary precession takes a long enough time (as on Earth). However, in the most likely chance that there is no bright star near the pole, I don't see how a sextant could measure reliably the inclination of a blank point.

Perhaps the first method could be used, but with other objects in the sky (stars) in place of the Sun. Thus, if a given star's inclination does not change as it (apparently) revolves around the horizon, we are at the pole.

Are there any better methods, assuming a completely self-contained system (i.e. no external satellites)?


texts: What is the gravitational wave spectrum of an ellipsoid neutron star like?

texts: If the star is ellipsoid instead a sphere, the wave should be rich of harmonics, not only (2*orbital frequency). Can these harmonics behave the same way, i.e. they appear/disappear together and drift (if they can drift) toward the same direction? Or any of the harmonics can behave independently, e.g.: fundamental frequency remain the same and the 2nd harmonic drift to higher frequency? If they can behave independently, what is the reason that can cause such behaviour? Consider the star has precession and nutation movement.


texts: How to account for the effect of Star Formation History on the inferred Stellar Initial Mass Function?

texts:
I am studying a paper The effect of star formation history on the inferred stellar initial mass function and trying to reproduce the given results.
According equation (1) in the paper, the inferred IMF f(M) can be determined if the PDMF phi(M) and the star formation history S(t) is known. I am trying to calculate S(t) as per the description given in that paper in vain. Roughly, by what amount will the slope of f(M) change from phi(M) if S(t) is calculated? Example: If phi(M) = M^(-2.5), then by what amount will the index change in f(M) if S(t) is calculated and inserted into equation (1)?


texts:
For a high-school students, what are the ways to become an astrophysicist?

What should he/she take in college?

What is the career path to become an astrophysicist?


texts: How can X-rays be emitted from a black hole?

texts:
A black hole's gravity prevents light from escaping, how can a black hole emit X-rays? Visible light and X-rays are both electromagnetic radiation, shouldn't the black hole's gravity prevent X-rays from escaping?

What about Hawking radiation  that is predicted to be released by black holes.


texts: How does one interpret the definition of "accretion" in galaxy formation?

texts:
I am having trouble finding a solidifying definition of accretion when it comes to galaxy formation models and galaxy evolutions. Where as, in the context of satellite galaxies, dwarf galaxies, or gasses.

For example, how do interpret the sentence "Even
dwarf and Milky Way-sized halos do accrete new mass at low
redshifts".

Does this mean that they "gain" new mass or does this mean they "leak" new mass?


texts: Largest body in the solar system that a baseball thrown by a professional pitcher could escape

texts: What is the largest (most massive) known body in the solar system that a professional pitcher could throw a baseball off of, i.e. that has an escape velocity lower than ~102 MPH? (45.33 m/s)


texts:
I often hear that Earth is a unique planet because it has life. We also see a proper balance between plants and humans and other animals. Why is life not possible on another planet? Often people say because the environment of other planets is so different from the earth and it's hard to find a planet like ours. That seems pretty satisfactory; I can not live on Mars or Saturn.
On the other hand, I find it little misleading. Why do we imagine ourselves on other planets to see if life is possible on other planets? There might be different creatures that are used to different environments. There might be creatures that are adapted to ${\rm H_2SO_4}$.
I have two questions. First is my reasoning true? And if so what makes life rare on other planets or makes the earth so unique?


texts: How can I download all of this JPL MRO imaging data at once?

texts:
There are several files. I think that they all needs to downloaded to have the complete dataset. Is there a particularly good way to download them all in one shot?

https://pds-imaging.jpl.nasa.gov/volumes/mro/release50.html

The page shows over 100 individual icons, one for each volume.


texts: I am NOT an astronomy person, so this may be a dumb question, however I have recently found a tripod that appears to be for star tracking as far as I can guess. I would like to know the type of tripod and if possible the brand as it is not labeled and I do not know how to operate it.


texts: Why do the gas giants in the Solar System have comparatively large orbits compared to the inner planets?

texts: Ever since I observed the depictions of the Solar System, I was obsessed with the question of why the gas giants (outer planets) have very large orbits, compared to the planets that are closer to the Sun. Is it because of their mass or something I have ignored?


texts: From what distances do the atoms in you come from?

texts:
If the atoms of a human come from stars, comets, nebulas and magnetrons, then what is the greatest distance that two atoms of a human can possibly have been away from each other previously? Perhaps the distance could be further than 4 million light years, because two galaxies further than Andromeda could have fallen into the Milky Way in the earlier universe? is that correct?
Am I way off? Could it be 5 billion light years?


texts: What class of elements are providing the many electrons needed to make the H- ion?

texts: Continuous absorption by the H- ion reaches its maximum in the cool atmospheric layers of G stars.  At these temperatures, most of the hydrogen atoms are neutral; but what class of elements is providing the many electrons needed to make the H- ion?


texts: Where can I find good places to watch stars?

texts: Where can I find good places to watch stars near me? I live in Leicestershire, England and am looking for good places to watch the sky nearby.


texts: How was the astrometry of the famous 1919 solar eclipse confirmation of General Relativity calibrated and verified?

texts:
The new New York Times article The Eclipse That Made Einstein Famous describes several events and discussions on the hundred year anniversary of the the 1919 solar eclipse and verification of the deflection of light by the Sun as predicted by General Relativity. The roles of Albert Einstein, Arthur Eddington, and others are discussed in the article, the play performed at the Royal Astronomical Society in London, in the Nature Physics article A hundred years of the first experimental test of general relativity and the book No Shadow of a Doubt; The 1919 Eclipse That Confirmed Einstein's Theory of Relativity by Daniel Kennefick.
The instruments used for the measurement are shown in the illustration and photograph below.
My question is about the astrometric technique used, and the calibration and verification.
The instruments are long and laying on their sides, viewing the eclipse and the stars near the Sun by reflection in coelostats (mirrors in front of telescopes, moved by clockwork mechanisms).
I can imagine several sources of instrumental and experimental errors due to variations in field distortion and magnification, presumably the measurement was done by comparing the eclipse images with similar images taken by the same instruments of the same field of stars in the same position in the field of view a few months later, at night, in the dark, in order to show that the tiny deflections were not due to variation from one instrument to another.
Is that actually how it was done? Was the experimental set-up left in-place between day and night measurements, or was it packed up and moved?
Was the flatness of the coelostat mirrors independently confirmed somehow?

Images from the new New York Times article The Eclipse That Made Einstein Famous

Einstein’s theory suggested that starlight would bend near a massive body like the sun.CreditChronicle/Alamy
In Sobral, Brazil, two coelostats with movable mirrors were used to direct images of the eclipsed sun into a pair of horizontal telescopes.
Credit Royal Observatory, Greenwich/Science Museum Group


texts: Who is considered as the father of modern astronomy?

texts: Googling is giving me both Galileo Galilei and Nicolas Copernicus as the answer. I am sorry and will remove this question if it is an opinion based question.


texts: I'm having a debate about how bright Martian nights would be, in terms of both the sky itself and ground illumination. This answer seems to indicate that the stars would be only dimly visible, and wouldn't provide enough light to see by. However, the question remains of how much illumination the moons would provide. I've seen it said that Deimos would appear about as bright as Venus does from Earth, and that Phobos would be about twenty times brighter, but it's not clear to me how that compares to e.g. our own moon's illumination. So how bright would it look? Would it be enough to see by?


texts: Why do some nebulae look like the billowing clouds? Wouldn't that require something like a viscosity in empty space?


texts: When was the martian dichotomy first observed?

texts:
The North and South hemispheres of Mars are very different one from another. They have different elevations, different crust thickness, different surface ages. This is known as the martian dichotomy.
When was this striking difference between the two hemispheres first observed?


texts: How well is Earth’s motion through the universe quantified?

texts: If I had a time travel machine that could drop me into any point in space and time, could I accurately predict earth’s “position”?  I know position is an improper term.  Would it be possible to know exactly where to land so that you are at the same spot on the surface of Earth as when you “departed”?


texts: How to plot orbit of binary star and calculate its orbital elements?

texts:
I have a set of dates, position angles ($\theta$) and angular separations ($\rho$) for visual binary star. For example:

1994.3132  57.0    0.097
1996.1783  73.4    0.051
2006.1938 182.0    0.126
2009.2597 192.9    0.152
etc.

What are algorithms to calculate orbital elements and to plot the orbit of the binary star?

Are there available codes (or programs) for this calculations?


texts: Can you still see Polaris even if you are in the south pole?

texts: I haven't been to south pole but can the Polaris still be viewed if the viewer is in the south pole? Or this question makes no sense at all?


texts: Is it possible to completely see the edge of a half moon at night?

texts:
Some days ago, about 1 ~ 1.5 hours after the sunset I could see a very bright half moon, and the interesting part is, I think I could see the edge of the dark half of the moon, i.e. a whole circle, but with very little contrast to the surrounding black space. It was very weak.
I'll use my impressive graphic design skills to try to explain it better:

The line I'm talking about is that grey one on the left, closing the moon.
My hypotheses are:

My brain made it up, as if it was trying to "close the circle"
The earth was lighting the moon up, as in: light from the sun was hitting the earth and being re-emitted to the moon (as a very bright moon can actually provide you enough light to see in the dark).

Thanks!


texts: Does the Earth's orbit around the sun exhibit nodal precession, as does the moon's around the Earth?  If it does, that must mean that the ecliptic is in a periodic wobble with respect to the celestial sphere?


texts: Tools and algorithms for angles-only orbit estimation

texts: I've seen discussion threads where amateur astronomers estimate a satellite's orbital parameters from angles-only telescope observation.  Are there any community tools or algorithms to help with this math? It's not a trivial problem to solve.


texts:
As I understand it, light that is emitted from a source is not imparted with the motion of the source and so always follows a "straight line". If this is correct, I am having a difficult time conceiving how the Lunar Laser Ranger experiments can detect photons.

In this experiment, a pulse of light is aimed towards a retro-reflector and it is reflected back. It takes about 2.5 seconds round trip and due to diffraction, the returning pulse covers a circle of approximately 20kms in diameter.

The Earth's orbital velocity is approximately 30km/s and in the time the pulse takes to make the round trip, the detector would be 75kms further along the Earth's orbital path. If my first paragraph is accurate, and the light pulse is not imparted with the Earth's orbital velocity, then how is detection of the returning light pulse achieved?

I hope this makes sense and thank you.


texts: Is Sahara desert a good place to build radio/optical telescopes?

texts:
At least Atacama Desert of northern Chile is a good place to build telescopes.

VLT and ALMA locate there.

What about Sahara desert?

http://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array

http://en.wikipedia.org/wiki/Very_Large_Telescope


texts: How many of the whole zodiac constellations can be seen in one single night?

texts:
As far as I understand, since the the 12 zodiac constellations (astrological signs) 'surround' the earth, hence it's possible to see by naked eyes a group of 6 astrological signs (only) simultaneously - from one hemisphere.

Assuming it's correct, my question is how many of the 12  zodiac constellations are possible to see in one single night?

Since the earth moving constantly, it seems that the answer depends on the time and season, but assuming that the day and the night are equal in time (March 21th), what will be the answer? To my logic it should be 12 but I am not sure about it.


texts: Can a telescope be built to focus on a point source star?

texts:
If a Kepler telescope were built to focus on one point source star at a time, would it provide more information, or did Kepler capture virtually every photon from any given star anyway?

In order to study known transit events more closely one star at a time, to possibly detect moons or atmosphere or rings by resolving the transit light curve's shape better, is a larger aperture necessary or would a smaller field of view help? What field of view would be optimal for observing a single point source?


texts:
I've read various articles and books (like this one) stating that we are not certain about the geometry of the universe, but there were experiments on-going or planned that would help us find out.

Recently though, I've watched a lecture by cosmologist Lawrence Krauss where he seems to categorically assert that the universe has been proven to be flat by the BOOMERanG experiment. Here's the relevant portion of the talk.

I've looked around and there are still articles stating that we still don't know the answer to this question, like this one.

So, my question is two-fold:

Am I mixing concepts and talking about different things?
If not then is this evidence not widely accepted by some reason? What reason would that be?


texts:
Where is the Solar system's barycenter located?
The solar system as a whole, Where is the center of the mass for the combined mass of the Sun, inner planets, and gas giants, is it inside the Sun? Is there an AU measured distance of it?


texts: Determining sunrise and sunset times based on azimuth and elevation

texts:
If I observe the sun and measure the local azimuth and elevation, and I also have my latitude, can I calculate the local sunrise and local sunset times? If so, how would I calculate it?

Further, can the same calculations be used for the moonrise and moonset?


texts:
I just read When a star becomes a black hole, does its gravitational power become stronger? and it confused me a bit;

I always thought black holes are supermassive and that is why they bend space-time. But it is said therein that the black hole is less massive than the star that created it (and it seems logical if we think about that - indeed, the star exploded and released a lot of matter).

Thus my question: How can a black hole bend space-time more than the star which created it?


texts: Milky Way as seen by the human eye: where exactly do those photons come from?

texts:
I'm asking here about the diffuse glow seen by the human eye, when looking at the Milky Way.

Where do those visible photons come from exactly?

the surface of a star?
starlight bouncing off something (dust or a molecule)?
emitted by gas in the interstellar medium?
all of the above?


texts: Is there any way to distinguish the doppler redshift from a distant galaxy from the probably much greater cosmological redshift?

texts: Is there any way to distinguish the doppler redshift from a distant galaxy, caused by its initial recessional velocity relative to this galaxy, from the probably much greater, cosmological redshift, caused by the expansion of space?


texts: Singularity in Laplace Method for Orbit Determination

texts:
I have a question about Laplace angle-only method for orbit determination where the line of sight vectors are being interpolated. I read somewhere that the method fails (due to a matrix being singular) when the observation site is in the motion plane of the observed body, but failed to see proof for that.
Could anyone explain to me why is that?


texts:
If a spacecraft slingshots around a planet P (with escape velocity V) at an angle $\theta$, I understand that the resulting velocity is $${ v }_{ 2 }=({ v }_{ 1 }+2u)\sqrt { 1-\frac { 4u{ v }_{ 1 }(1-cos(\theta )) }{ ({ v }_{ 1 }+2u)^{ 2 } }  } .$$

However, this equation does not involve the mass of the assisting planet, nor the distance/altitude from which the spacecraft must slingshot from. After reading the answer to To what extent could a single Triton flyby slow down a direct Hohmann transfer to Neptune for NOI?, I have a few questions:

How is the formula for the bent angle and eccentricity derived?
What exactly is the geometry behind the maneuver? More specifically, where does the hyperbola come from?
How is the formula for the turning angle, $\delta =2\sin ^{ -1 }{ \left( \frac { 1 }{ 1+\frac { { r }_{ p }{ v }_{ \infty  }^{ 2 } }{ \mu  }  }  \right)  } $ derived?

Please note that I'm a high school student with a knowledge of Calculus I & II, and that visual diagrams would be greatly helpful.


texts:
Is the Celestron astromaster 130 EQ Model able to see nebulas and galaxies?
If this telescope is not able to see nebulae, please suggest me the best one telescopes for nebulas.


texts: How do the sun's light rays come to the world?

texts:
How do they come to the world? One of my friends who is a flat earther told me about how the rays seem to gather at one point, which sort of proves that the sun is close to us and not very big, in his opinion. He thinks that the rays should come parallel, as the sun is much bigger than the world. We were also taught that they come parallel, as shown in the image.

However, what had me thinking is that the sun isn't that big from our point of view. When we look at it, it just seems like a small marble, and this makes it a small spherical light source. It being small makes it act like a point light source in my opinion, and this means the light rays do not come to the world as in the image, but with different angles. I also think that to see a spherical light source's light rays coming parallel toward us, the source must cover all of our horizon, but this is not the case for the sun since it seems just like a marble from the earth.
Can anyone please explain this to me? Is the image not the correct way to teach this?


texts: To which extent is optically thick photon transport related to conduction?

texts:
When speaking about energy transport, the textbook, physics-101 always lists three possibilities:

radiation
convection
conduction

Now when studying radiation transport in (stellar) atmospheres and of course astronomy & astrophysics in general, we are always concerned about the photon mean-free path $\lambda_{mfp}$. When $\lambda_{mfp}$ becomes too small compared to a scattering or absorption mean-free path, the equations of radiation transport turn into a diffusion equation for the photon intensity $I_{\nu}$ at frequency $\nu$, so that we get
$$ \partial_t I_{\nu} \sim \nabla (D \nabla I_{\nu})$$
where the diffusion coefficient $D$ in the optically thick limit is proportional to density $\rho$ and opacity $\kappa_{\nu}$, $D \sim (\rho \kappa_{\nu})^{-1}$.

Now I want to understand differences of this process to conduction, which is similarly modeled with a diffusion equation, but different underlying transport physics. In solid state physics lectures one often derives the heat and transport of crystals, which then is given by the properties of how well phonons can transport momentum inside the crystal.

So finally, my question:
As we go deep into a star, a white dwarf or a Jupiter-like planet, the efficiency of optically thick photon transport becomes less and less.
So in our transport equations, do we need to replace photon transport terms at some point brute-force by phonon/sound wave energy transport terms, or do they arise naturally when photons are scattered off phonons?

I'll add a TLDR:
Is optically thick phonon transport and conduction like in solid state physics sometimes the same?


texts: Is it possible that a binary star doesn't exceed its Roche lobe and so when the second star becomes a red giant, instead of accreting some of its plasma onto the white dwarf that it becomes a white dwarf itself which causes there to be no supernova?


texts: Stars explode when they die and blast heavy elements into space.  Do galaxies do the same thing?


texts:
Performance of astronomical mirrors that are exposed to the environment for long periods of time can experience a slow degradation of performance. They usually need to receive some kind of regular maintenance, which may involve cleaning and/or re-coating.

While I'm told that the aluminum degrades and must be replaced from time to time, this is not consistent with my understanding of the behavior of aluminum in air. I'm pretty sure that a freshly evaporated layer of pure aluminum will quickly develop a native oxide layer of perhaps 20Å of aluminum oxide as amorphous $\text{Al}_2 \text{O}_3$ (alumina) which is then pretty much impermeable to diffusion of anything else the atmosphere might expose it to, including various pollutants.

I can understand that it might in some cases ultimately be simpler to strip and replace the aluminum after a number of cleanings due to accumulated damage from the cleaning, but is there any evidence that the aluminum must be replaced due to chemical degradation of the aluminum itself?

I found this article, Reflectivity Degradation Rates of Aluminum Coatings at the CFHT, Magrath, B. 1997, Pub. Ast. Soc. Pac. 109, 303 that seems to show that - at least at one observatory location - a representative test mirror exposed to the observing environment (in the dome) that was washed once a month showed no significant degradation in reflectivity over 32 months, similarly to a mirror that remained protected but not cleaned.

However, the test mirror that was exposed and not washed showed a continuous loss in reflectivity, dropping by about 10% over the same period. A fourth test mirror undergoing regular $\text{CO}_2$ cleaning lost about 5% reflectivity.

This is a small, limited test of course, less than three years, only one location, one wavelength, and only one parameter (reflectivity). But it gives a bit of support to the idea that while mirrors get dirty and require regular cleaning, the aluminum itself may not actually deteriorate.

So I'm asking: Do primary mirrors in large observatories undergo regular removal and re-coating of the aluminum? Why?, where "why" addresses the specific need for the removal and replacement. If these primaries actually do receive regular re-coatings of aluminum, is it because the aluminum actually degrades?

I'm looking for an answer that carries some backup references. If just for example, your answer is of the form You silly goose, everybody knows aluminum tarnishes like the Dickens!, please back it up with a reference to measurements of aluminum tarnishing. Thanks!

From Magrath 1997:

GIF ("blink comparator")

From http://global.kyocera.com/fcworld/charact/chemistry/chemiresist.html - alumina can potentially be remarkably resistant to chemical attack compared to other materials - note logarithmic scale.

The individual figures:


texts: Why is there a gap in this image of supernova discoveries?

texts:
I came across this gif showing supernova discoveries from the late 19th century to 2010. Here's the data in 2010:

Notice that there's a prominent region shaped like an inverted U in which there are few detection points, which I have crudely enclosed:

Why is this? Is it an artifact of detectors simple not observing that part of the sky, or is there some underlying astronomical reason?


texts: What are the apparent visual magnitudes of Spica A and Spica B?

texts: What would be the (theoretical) apparent visual magnitudes of Spica A and Spica B (since they are too close together to be resolved telescopically)?  The Spica System is 77 parsecs away, and the combined apparent visual magnitude of the two stars is 0.97 at maximum (presumably when the stars are not eclipsing each other).  Their orbital parameters and respective luminosities, temperatures, and radii are given on Wikipedia: https://en.wikipedia.org/wiki/Spica


texts: Is there a preference for orbital planes of planetary systems to be aligned with the galactic disk?

texts:
I'm not sure for how many planetary systems we have a fairly good idea of the inclination and "argument of periapsis" of the orbital plane. I'm assuming there are a number of them that we can estimate due to co-planar assumptions in a multi-planet system or some other means.

I am asking if there are enough "known" orbital planes that we can have some statistical idea whether or not the orbital planes are somewhat aligned with the galactic plane or whether local forces would dominate galactic orbit angular momentum. (I'm thinking the latter is true.)

We would have to keep in mind of course that a system "directly above" us and parallel to the galactic plane would be "face on".


texts:
I have a Dobson Omegon with a 640mm focal length and a 102mm aperture.
My finderscope is broken but I can do without.
I have located the planets with the naked eye but I do  I do not see them through my eyepiece.

I can focus perfectly on the moon, using a 20mm eyepiece. (I have a 6mm eyepiece as well.)

How should I proceed?


texts: Could the unseen companion of HR 6819 be a close binary system?

texts:
Recently there was an announcement of a black hole candidate in the HR 6819 system (ESO Instrument Finds Closest Black Hole to Earth). In the proposed system, the black hole forms a close binary with the B3III primary of the system, and a Be star is located on a wide outer orbit forming a hierarchical triple:

 ┌ B3III star
┌┤
│└ black hole
┤
│
└ Be star

Reading through the research paper Rivinius et al., 2020, it is mentioned that there is no X-ray emission detected from the system indicating that it is either not accreting significant quantities of material, or that it may not be a black hole. The paper notes that the companion cannot be a single main-sequence star (which they estimate would be of spectral type B7 or earlier) because this would appear in the spectral lines, which given the mass leads to the inference that the companion is a black hole as it is too massive to be a neutron star or white dwarf.

As far as I can see, I don't see any mention of the possibility that the companion could itself be a close stellar binary, i.e. the following architecture:

 ┌ B3III star
 │
┌┤
││┌ close binary, star 1
│└┤
│ └ close binary, star 2
┤
│
│
│
└ Be star

A binary of near-equal-mass stars would have lower luminosity than a single star of the same total mass, which might help it avoid detection.

I'm wondering if the configuration would be possible given the short period (40 days) of the companion's orbit, but maybe the data is sufficient to rule this out.


texts: Why can we observe the Cosmic Microwave Background no matter the direction we look?

texts:
I often read that the CMB was released from everywhere in the Universe, in every direction.

If that statement is true, can someone elaborate what "everywhere in the universe, in every direction" means ? If not, why can we observe it in every direction ?


texts: I've read that there are 4 distinct although related forms of AGs : Seyferts, Quasars, Radio and Blazars. Are there any other forms possible? Also do these forms ever intermix to give something new?


texts:
At the moment (01-04-2020 09:36) the Moon is situated in Gemini:

"The Moon is currently in the constellation of Gemini. The current Right Ascension is 06h 37m 56s and the Declination is +23° 42' 09”." theskylive.com, 2020.

If there are 12 houses (zodiac) and Right Ascension is in a 24hr format how is the moon calculated to be in Gemini?

The calculation i'm using has it in Cancer. This is obviously a mistake but here's how i'm getting it:

Aries 0h 0m 0s
Taurus 1h 51m 39s
Gemini 3h 51m 16s; <- (Moon is  actually in Gemini)
Cancer 6h 0m 0s; <- (here's where ive got the    moon at 06h 37m 56s)
Leo 8h 8m 44s;
Virgo 10h 8m 21s;
Libra 12h 0m 0s;
Scorpio 13h 51m 39s;
Sagittarius 15h 51m 16s;
Capricorn 18h 0m 0s;
Aquarius 20h 8m 44s;
Pisces 22h 8m 21s.

(Courtesy of https://astronomy.stackexchange.com/a/27488)

How have I misunderstood right ascension and how would I derive Gemini from RA 06h 37m 56s?


texts: How significant is a planet's density to the formation of life?

texts:
I'm doing some writing set on a fictional earthlike planet that for reasons needs to be substantially larger than Earth but can't have substantially higher gravity. I've been able to compromise with a planet that's 6x the circumference, having a surface gravity of 1.5G, yielding a density of about 4700kg/m^3.

This is quite a bit (~15%) less than Earth and Venus, but (20%) more than Mars. It would proportionally have less heavy metal, meaning less iron for a protective magnetic field. I would like this planet to have some basis in reality - could such a planet be earth-like, and is there a definitive range of planet densities where life as we know it could exist?


texts: What is the Age Difference Between Earth & Jupiter?

texts:
What is the age difference between Jupiter & Earth?

Which planet was formed first, or were they formed at the same time?


texts: I'm studying Astrophysics and I have some video's from a past course. I'm currently studying the reionization of the universe. At the current point in the class, the instructor is talking about quasars and the redshift at which the Lyman-Alpha forest disappears. This appears to occur at a redshift greater than 6. The instructor goes into finding quasars with z > 6.5. He states that quasars that far away, "They're only emitting infrared light.". I don't understand that statement. Does the instructor mean they are only visible in IR or those very old quasars only emit in IR? Why would quasars only emit in IR? I understand why we'd only see IR from them.


texts: Can someone tell me the contribution of s-, r-, and p-isotope processes to copper?

texts:
I have looked for relevant information in the paper Chemical evolution with rotating massive star yields
II. A new assessment of the solar s- and r- process
components before, but unfortunately, it only records the element gallium.


texts: What might some examples be of radio telescope interferometric arrays made from "cheap components relying on massive computing power"?

texts:
This answer mentions that there are some interferometric radio telescope arrays

  ...consisting of very cheap components relying on massive computing power to retrieve the signals from noise...

The radio interferometers that normally come to mind for me are the VLA and especially ALMA type, where there are only dozens of dishes, each one extremely high-tech and chock full of analog and digital electronics, often linked by high speed fiber optic cables.

What might examples of arrays made from "cheap components relying on massive computing power" be?


texts: How to make projection from altitude and azimuth to screen with screen coordinate system?

texts: Thanks to @ohoh for helped translate ra and dec into alt and az. Now that I have this data(altitude and azimuth), how can I plot it in something like this, with the coordinate system going like this?


texts: Python: Find brightest pixel in fits-file and ignore brighter artefacts

texts:
I have 4000 fits-files images from SPITZER, each containing the same star over a time period. Each image is a photmetry cube of 32 pixel * 32 pixel * 64 consequent time frames. I need to look through all the single frames and order the pixel by brightness. Not hard to do with Python, but sometimes I have in the frames short-lived events/artefacts which are brighter than the brightest pixel of the star (see below). These artefacts last only over one or two consequent time frames

How can I easily correct for the artefacts? Is there an astropy/pyfits package that does this? Or some kind of bad pixel flagging in SPITZER (I know that Kepler-images have flagging of bad pixel)?

Optional: It would be convenient to have the code in vectorized form, avoiding loops, so that I save computtional time

Fig: In the left frame everything is normal, in the right frame, in the top right corner you see one of the artefacts, having a value below a saturation treshhold